The invention relates to a marine drive having two counter-rotating surface operating propellers.
The present invention arose during development efforts directed toward a marine drive enabling increased top end boat speed. This is achieved by raising the torpedo or gear box out of the water to reduce drag, and by using two counter-rotating surface operating propellers. Surfacing drives are known in the art, for example U.S. Pat. No. 4,871,334, column 3, lines 35+.
The drive has a transom X-dimension defined as the distance along the transom of the boat between the axis of rotation of the engine-driven shaft and the bottom of the boat. The drive has a vertical X-dimension defined as the vertical distance between the axis of rotation of the engine-driven shaft and the plane of the bottom of the boat. The drive has a shaft-spacing dimension defined as the distance between the axis of rotation of the upper input shaft in the upper horizontal bore and the axis of rotation of the concentric counter-rotating. propeller shafts in the lower horizontal bore. The drive has a surfacing dimension defined as the vertical distance between the bottom of the torpedo and the plane of the bottom of the boat when the propeller shafts are parallel to such plane.
The present invention provides structure enabling a surfacing drive without increasing the X-dimension. This in turn enables the boat builder to provide a surfacing drive without otherwise having to mount the drive high on the transom and the engine high in the boat. The invention provides various desirable combinations of defined X-dimension, shaft-spacing dimension, and surfacing dimension.